1. Field of the Invention
The present invention relates to a brushless motor system, and more particularly, to a brushless motor system with capacitors.
2. Description of the Prior Art
DC brushless motors are widely used due to their simplicity of design, durability and efficiency. Many of the motors used in computer storage devices, such as the spindle motors of hard disk, CD-ROM, CD-RW and DVD devices, all employ DC brushless motor technology. As computing speeds grow, so, too, does the demand for faster access times of computer storage devices. This places greater demands of speed and stability on the spindle motors of these devices. Therefore, controlling a spindle motor to make it both fast and stable has become an important subject in the field of storage device design.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art brushless motor system 10. The prior art brushless motor system 10 comprises a 3-phase brushless motor 12, a driver 14, and three Hall sensors 16. The brushless motor 12 comprises a rotor (not shown). The Hall sensors 16 are used to detect the rotor position. The driver 14 drives the rotor of the brushless motor 12 based upon the rotor position as detected by the Hall sensors 16.
As the rotor rotates, each of the Hall sensors 16 generates and sends two corresponding sensing signals to the driver 14. The sensing signals generated by the three Hall sensors 16 are denoted as H1+, H1xe2x88x92, H2+, H2xe2x88x92, H3+, and H3xe2x88x92. The driver 14 outputs 3 phase currents A1, A2, and A3 to drive the brushless motor 12 based upon the sensing signals generated by the three Hall sensors 16.
Please refer to FIG. 2. FIG. 2 is an ideal time sequence diagram of the sensing signals H1+, H1xe2x88x92, H2+, H2xe2x88x92, H3+, H3xe2x88x92 and the 3 phase currents A1, A2, and A3. As the rotor rotates, the sensing signals H1+, H1xe2x88x92, H2+, H2xe2x88x92, H3+, and H3xe2x88x92, which have the same wave shape but with different phases, are generated by the Hall sensors 16. The corresponding 3 phase currents A1, A2, and A3, which also have the same wave shape but with different phases, are generated by the driver 14 according to these sensing signals. Ideally, the two sensing signals generated by the same Hall sensor 16 should have the same DC bias and should be symmetrical with respect to each other. Under these ideal conditions, the driver 14 should generate the correct 3 phase currents A1, A2, and A3, with no DC biases, based upon these ideal sensing signals, resulting in the smooth operation of the brushless motor 12.
Please refer to FIG. 3. FIG. 3 is a realistic time sequence diagram of the sensing signals H1+, H1xe2x88x92 and the phase current A1. Generally, the wave shape of the sensing signals does not match the ideal wave shape shown in FIG. 2. Due to inaccuracies of the ion-implantation process that is used to make the Hall sensors 16, or environmental effects such as temperature, the DC biases in the two sensing signals generated by the same Hall sensor 16 are not usually the same. For instance, the DC bias Dc+ in the sensing signal H1+ will probably be different from the DC bias Dcxe2x88x92 in the sensing signal H1xe2x88x92. This differing bias will cause the motor driver 14 to generate the output phase current A1 with a DC bias. Likewise, the sensing signals H2+, H2+, and H3+, H3xe2x88x92 with different DC biases will also cause the motor driver 14 to generate the output phase currents A2 and A3 with DC biases. As the output phase currents correspond to the torque of the motor, biased currents will generate an unbalance torque. As a result, the brushless motor 12 will not run smoothly.
It is therefore a primary objective of the present invention to provide a brushless motor system with capacitor devices to solve the above mentioned problem.
In a preferred embodiment, the present invention provides a brushless motor system comprising:
a brushless motor comprising a rotor;
at least one sensing circuit for detecting the rotor position, the sensing circuit comprising:
a Hall sensor comprising two output ports; wherein as the rotor rotates, the Hall sensor will generate a sensing signal at each of the two output ports; and
a capacitor device for each of the two output ports of the Hall sensor, the capacitor device connected in series with the output port; wherein the two capacitor devices are used to filter out DC biases in the two sensing signals; and
a motor driver connected to the two capacitor devices for driving the rotor of the brushless motor according to the two sensing signals from the two capacitor devices.
It is an advantage of the present invention that the brushless motor system comprises the capacitor devices, which filter out the DC biases in the sensing signals, so that the brushless motor will run fast and smooth.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.